#23761: fix: suppress partial NO_REPLY tokens at lifecycle boundary

## Problem When the model streams `NO_REPLY` as multiple tokens (e.g. `"NO"` then `"_REPLY"`), the `lifecycle:end` event can fire while the buffer only contains the partial prefix. `isSilentReplyText()` returns `false` for `"NO"`, causing it to leak to connected clients as a real assistant message. This is particularly visible on node clients (VS Code extensions, mobile nodes) that display every `chat-final` message as a bubble — users see random `"NO"` or `"NO_"` messages appear. ## Fix Add a partial-prefix check in `emitChatFinal`: if the buffered text is a strict prefix of `SILENT_REPLY_TOKEN`, is shorter than the full token, and contains only `[A-Z_]` characters, treat it as a silent reply and suppress it. The check is deliberately conservative: - Minimum 2 characters (avoids matching single letters) - Must be strictly shorter than the full token (full match already handled by `isSilentReplyText`) - Only uppercase letters and underscores (won't match real messages) ## Testing Tested in production with a VS Code node client (Pawr) over multiple days. No more leaked partial tokens. Fixes #3340 <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds logic to suppress partial `NO_REPLY` tokens that leak when the model streams the token across multiple chunks and `lifecycle:end` fires before the complete token arrives. The fix checks if buffered text is a strict prefix of `SILENT_REPLY_TOKEN` before emitting `chat-final` events. - Prevents partial tokens like `"NO"` or `"NO_"` from appearing as assistant messages in client UIs - Conservative approach with minimum 2-char length and character class validation - Complements existing `isSilentReplyText()` which handles complete tokens <h3>Confidence Score: 4/5</h3> - Safe to merge - addresses real production bug with conservative logic - The fix correctly addresses the partial token leak issue with appropriate boundary checks. Logic has been tested in production. Minor style improvement suggested on regex flag but doesn't affect correctness - No files require special attention _{Last reviewed commit: abe3c10} <!-- greptile_other_comments_section --> _{(3/5) Reply to the agent's comments like "Can you suggest a fix for this @greptileai?" or ask follow-up questions!} <!-- /greptile_comment -->